Git, Fast and Distributed Version Control System Salimane Adjao Moustapha [email_address] http://theindexer.wordpress.com Ethos Technologies

Introduction

Summary What is git? Difference git and other SCMs Git Object Model Why git is better than X Benefits of using git for an engineer Benefits if using git repos in a company Sample git commands Conclusion

What is git?

Difference git and other SCMs

Git Object Model

Why git is better than X

Benefits of using git for an engineer

Benefits if using git repos in a company

Sample git commands

Conclusion

What is git? Distributed development. Strong support for non-linear development. Efficient handling of large projects.

Distributed development.

Strong support for non-linear development.

Efficient handling of large projects.

Difference git and other SCMs Other SCMs - Delta Storage Systems - Tracking file permissions and ownership Git - Snapshot of what all the files in your project look like in this tree structure, each time you commit. Track changes of the tree through time. - Tracking the content of the file, not the container

Other SCMs

- Delta Storage Systems

- Tracking file permissions and ownership

Git

- Snapshot of what all the files in your project look like in this tree structure, each time you commit. Track changes of the tree through time.

- Tracking the content of the file, not the container

Git Object Model The SHA All the information needed to represent the history of a project is stored in files referenced by a 40-digit "object name" that looks something like this: 6ff87c4664981e4397625791c8ea3bbb5f2279a3 This has a number of advantages among others: Git can quickly determine whether two objects are identical or not, just by comparing names. Since object names are computed the same way in every repository, the same content stored in two repositories will always be stored under the same name. Git can detect errors when it reads an object, by checking that the object's name is still the SHA1 hash of its contents.

The SHA

All the information needed to represent the history of a project is stored in files referenced by a 40-digit "object name" that looks something like this:

6ff87c4664981e4397625791c8ea3bbb5f2279a3

This has a number of advantages among others:

Git can quickly determine whether two objects are identical or not, just by comparing names.

Since object names are computed the same way in every repository, the same content stored in two repositories will always be stored under the same name.

Git can detect errors when it reads an object, by checking that the object's name is still the SHA1 hash of its contents.

The Objects Every object consists of three things - a type , a size and content . The size is simply the size of the contents, the contents depend on what type of object it is, and there are four different types of objects: A "blob" is used to store file data - it is generally a file. A "tree" is basically like a directory - it references a bunch of other trees and/or blobs (i.e. files and sub-directories) A "commit" points to a single tree, marking it as what the project looked like at a certain point in time. It contains meta-information about that point in time, such as a timestamp, the author of the changes since the last commit, a pointer to the previous commit(s), etc. A "tag" is a way to mark a specific commit as special in some way. It is normally used to tag certain commits as specific releases or something along those lines.

The Objects

Every object consists of three things - a type , a size and content . The size is simply the size of the contents, the contents depend on what type of object it is, and there are four different types of objects:

A "blob" is used to store file data - it is generally a file.

A "tree" is basically like a directory - it references a bunch of other trees and/or blobs (i.e. files and sub-directories)

A "commit" points to a single tree, marking it as what the project looked like at a certain point in time. It contains meta-information about that point in time, such as a timestamp, the author of the changes since the last commit, a pointer to the previous commit(s), etc.

A "tag" is a way to mark a specific commit as special in some way. It is normally used to tag certain commits as specific releases or something along those lines.

Blob Object A blob generally stores the contents of a file. git show 6ff87c466498...

Tree Object A tree is a simple object that has a bunch of pointers to blobs and other trees - it generally represents the contents of a directory or subdirectory. git ls-tree 6ff87c466498...

Commit Object The "commit" object links a physical state of a tree with a description of how we got there and why. git show -s --pretty=raw 6ff87c466498...

. -- README -- lib/ --inc/ --tricks.rb --mylib.rb

Why git is better than X Cheap local branching Complex merging Everything is Local Git is fast Git is small Easy to learn

Cheap local branching

Complex merging

Everything is Local

Git is fast

Git is small

Easy to learn

Benefits of using git for an engineer You can work offline on your notebook and track every changes you're doing to the codes without anybody noticing anything. You can work in parrallel on many tasks. You can make mistakes and erase your mistakes. You can edit commit and the commit will look like everything was done once. You can stash your local modifications and replay them later. You can pull from a collegue repo without the server and others being notified You become productive because instead wasting time copying, recoding, committing or updating codes, you can concentrate on changing the actual source codes. Intuitive commands. Creating patches easily (emailing patches easily). You can use git with subversion or cvs repositories. You don't have to have commit permissions to start making changes and tracking them. (patch, publish). One directory .git, no more deeper polluting directories like svn.

You can work offline on your notebook and track every changes you're doing to the codes without anybody noticing anything.

You can work in parrallel on many tasks.

You can make mistakes and erase your mistakes.

You can edit commit and the commit will look like everything was done once.

You can stash your local modifications and replay them later.

You can pull from a collegue repo without the server and others being notified

You become productive because instead wasting time copying, recoding, committing or updating codes, you can concentrate on changing the actual source codes.

Intuitive commands.

Creating patches easily (emailing patches easily).

You can use git with subversion or cvs repositories.

You don't have to have commit permissions to start making changes and tracking them. (patch, publish).

One directory .git, no more deeper polluting directories like svn.

Typical workflow

Benefits of using git repos in a company Better impressions on clients / partners Easy management of your repositories Saving disk space on your servers Less load on your servers Get more productive time from your engineers Saving Money

Better impressions on clients / partners

Easy management of your repositories

Saving disk space on your servers

Less load on your servers

Get more productive time from your engineers

Saving Money

Sample git commands git init git add . git commit git clone url git branch -r git stash git stash apply git checkout -b task1 master git commit -a -m “task1 solution” git diff --binary HEAD > tempPatch.diff git diff task1 HEAD~2 git reset –hard git status git-checkout master git merge task1 git-branch -d task1 git-rebase -i task1 task2 git fetch git push git reset HEAD~3 git revert

git init

git add .

git commit

git clone url

git branch -r

git stash

git stash apply

git checkout -b task1 master

git commit -a -m “task1 solution”

git diff --binary HEAD > tempPatch.diff

git diff task1 HEAD~2

git reset –hard

git status

git-checkout master

git merge task1

git-branch -d task1

git-rebase -i task1 task2

git fetch

git push

git reset HEAD~3

git revert

Projects using git Linux Kernel Android Fedora Perl Ruby on Rails Gnome ....

Linux Kernel

Android

Fedora

Perl

Ruby on Rails

Gnome

....

Tutorial http://www.kernel.org/pub/software/scm/git/docs/gittutorial.html http://git-scm.com/course/svn.html http://www.spheredev.org/wiki/Git_for_the_lazy http://excess.org/article/2008/07/ogre-git-tutorial/ http://gitcasts.com/ http://book.git-scm.com/5_git_and_email.html http://book.git-scm.com/5_customizing_git.html

http://www.kernel.org/pub/software/scm/git/docs/gittutorial.html

http://git-scm.com/course/svn.html

http://www.spheredev.org/wiki/Git_for_the_lazy

http://excess.org/article/2008/07/ogre-git-tutorial/

http://gitcasts.com/

http://book.git-scm.com/5_git_and_email.html

http://book.git-scm.com/5_customizing_git.html